Head mounted displays which generally allow for the simultaneous viewing of visual information and/or images generated by a computer or other source with and/or superimposed on a direct viewing of an external scene are well known. Such head mounted displays find utility in many areas, such as training, machine control, or entertainment. Such systems have found particular utility in military applications where information must be supplied to vehicle operators and weapons controllers. Aircraft pilots find such systems useful to furnish information relating to aircraft operation, weather radar presentations, maps, weapons aiming, and other such information.
In some systems, the visual information or visual images are superimposed on an optical combiner mounted on the head gear, sometimes a helmet visor, in view of the eye of the wearer, i.e., the observer's line of sight. These visual images may be derived from a variety of display sources including cathode ray tubes, fiber optic displays, flat panel liquid crystal or electroluminescent devices, some including image enhancers, and even photographic projectors operating with an appropriate optical relay system, all of which may supply the observer with visual information. The demand for smaller systems on the head with lighter weight requires use of the new micro miniature displays, measuring less than 1 inch across the diagonal. The field of view demanded, however, remains steady, or increasing, so this requires a very fast (low F/#) optical collimator.
FIG. 1 shows a current optical relay system. It is a lightweight system utilizing flat panel displays. However, there is a great loss in the throughput from the flat panel display to the eye, because the beam is transmitted once and reflected once at the beamsplitter, which results in at least 75% throughput loss. This then requires more power for the image source on the wearer's head which made the optical system heavier. This was an added burden for manufacturing costs as well as weight requirements. Another configuration of an optical system is described in U.S. Pat. No. 5,576,887. There is such a large tilt angle on the aspheric toroid in this design that the field of view is aberration- and space-limited. Further, this design as well as other current designs has low optical power and a much larger display with larger pixels was required. U.S. Pat. No. 5,706,136 discloses a more compact optical system, but it has three anamorphic surfaces which are very difficult to manufacture and does not correct for color aberrations. U.S. Pat. No. 5,818,641 also discloses a compact image display, but again does not teach any capability of correcting for color aberrations from the solid prism. Both of these systems can only support a small exit pupil, which means the optical system must be held very steadily in front of the eye. It would be desirable to make the exit pupil three times larger (making the system 1/3 the F/#) in order to mount the display on the head and allow for misalignment and movement of the eye. Furthermore, the above mentioned optical systems do not have the ability to use a high resolution display.
It would be desirable if a lightweight and smaller optical system with high throughput existed. It would be desirable if a cost efficient and optical system without positioning restraints existed. It would be desirable if less complex color correcting optical system existed. It would be desirable if an optical system existed with the ability to use a high resolution display. Further, it would be desirable if a less complex optical system overall, but equally operable optical system existed.